The detection of oxidized proteins, lipids and DNA/RNA in human as well as animal and cellular models of neurodegenerative diseases has been documented. In the last decade additional chemistry based on the formation of reactive nitrogen oxides, byproducts of nitric oxide reactivity have been also documented by the detection of tyrosine-nitrated proteins mostly in the inclusions that characterize Parkinson's and other related diseases. Recent data has also indicated that reactive nitrogen oxides convert the free amino acid tyrosine to 3-nitrotyrosine. This unusual amino acid can be also formed in the CNS following the proteolytic degradation of nitrated proteins. Tyrosine is an important amino acid in the CNS since it serves as the building block for the formation of dopamine. We hypothesize that 3-nitrotyrosine interferes primarily with dopamine formation and tyrosine metabolism. Support for this hypothesis is derived from the sound documentation that 3-nitrotyrosine injected into rodent striatum selectively injures dopaminergic neurons. Another unrecognized feature of 3-nitrotyrosine may be the interference with mitochondrial respiration leading to the decline in ATP synthesis and additional production of reactive species. Preliminary data have also indicated a specific 3- nitrotyrosine-dependent disruption of microtubule assembly leading to the formation of soluble and insoluble protein aggregates. To test the critical aspects of these hypotheses we propose to evaluate the following: 1) determine if 3-nitrotyrosine interferes with the production, metabolism and biology of dopamine and tyrosine, 2) evaluate if 3-nitrotyroinse interferes with mitochondrial respiration and function and 3) examine if the formation of alpha/beta-tubulin aggregates resulting from the specific incorporation of 3-nitroyrosine into a-tubulin serves as a building block for the aggregation and/or fibrilization of alpha-synuclein. An array of biochemical, pharmacological, and molecular approaches that are already in place will be employed to perform the proposed experiments. The proposed experiments will evaluate the critical role of the endogenously generated unusual amino acid, 3-nitrotyrosine, as a central mediator responsible for alterations in fundamental regulatory pathways in dopamine metabolism, oxidative phosphorylation, and protein aggregation, which constitute well-recognized molecular targets responsible for neuronal injury and death in Parkinson's disease and related disorders. Overall a novel and previously unrecognized biological chemistry resulting from the formation of a modified amino acid, 3-nitrotyrosine, will be investigated in order to uncover multifaceted but potentially interrelated pathways that promote neuronal dysfunction in neurodegenerative disorders.